The present description relates, as its title indicates, to a support structure for solar collectors of the type used in cylindrical parabolic collectors to support the cylindrical parabolic reflector and the absorbing tube, characterized in that it comprises a main bearing structure on which a plurality of support arms for the parabolic mirrors is supported, said main bearing structure being formed by two rectangular lattice grids, a top one and another bottom one, in a parallel and overlaying arrangement, linked together by four laterally-disposed mini-lattices, in twos at each end, and by a plurality of external lateral ties bars and internal diagonal tie bars.
At the moment there are widely used devices for concentrating solar radiation based on cylindrical parabolic collectors, in which the solar energy capture area is formed by high-reflectivity parabolic mirrors that redirect the incident solar radiation and concentrate it on an absorbing tube located along its focal line. Inside the absorbing tube a thermal fluid that is usually oil, flows and absorbs the solar energy in the form of thermal energy, heating up to a temperature of around 400° C. The thermal fluid at this temperature is pumped towards a heat exchanger which generates steam that drives a turbine that is responsible for generating electricity
These cylindrical parabolic collectors require the reflective mirrors forming the energy capture area to have a great mechanical precision in their orientation towards the absorbing tube in order to achieve optimum heat transfer and to thus optimize the production of energy.
Furthermore it is essential for the structure that supports the parabolic mirrors and absorbing tube to have the necessary torsional and flexural stiffness to be able to maintain the precision of the focus of the energy capture surface on the absorbing tube, which is particularly important taking into account that solar collectors are usually accompanied by solar tracking mechanisms, in order to achieve optimum production of energy. Several attempts have been made to achieve this combination of torsional and flexural stiffness of the support structure of solar collectors with the capacity to move, by means of different technological solutions.
Devices such as those described in Patent WO 0102780 “Solar collector system” or in European patent 03815132 “Solar energy collector system with an absorber support mounting” that house the mirrors in a kind of box, a solution that has little torsional stiffness, especially if it is associated with a moving tracker device.
Other devices are known such as that disclosed in U.S. Pat. No. 5,058,565 “Solar concentrator device and support structure thereof”, which has a simple structure located above, with the problem that it casts shadows on the mirrors with the consequent reduction in energy performance, as well as the fact that the torsional stiffness obtained is not particularly good.
Other solutions have been sought. For example, U.S. Pat. No. 5,069,540 “Parabolic solar collector body and method”, US 2004/0118395 “Parabolic solar concentrator module” and US 2008/0087277 “Collector for solar thermal power station” claim solid or semi-solid single-piece support structures that have the drawback of their high cost, heavy weight and problems both with the transport between the production plant and the assembly site as well as the complex nature of on-site mounting.
A solution that is very commonly used resides in a structure formed by a longitudinally-disposed cylinder emerging from which are support arms for the mirrors as is described, for example in WO Patent 20070340048 “Support arm, cylindrical parabolic solar collector support and procedures to manufacture the arm”, which, in spite of its good performance, presents both manufacturing and transport problems in the central cylindrical unit and problems with the strength of the arms that only have several laminar folded pieces to reinforce them.
Another solution that has been used to try to improve the stiffness of the structure is to employ lattice structures, for example, such as that described in Spanish Utility Model U 200801470 “Structure for solar tracker”, that presents a lattice structure both of the tower and the arms of a photovoltaic solar tracker. The lattice structure offers the advantage of combining a light weight with excellent torsional stiffness, but has the drawback that for large size collectors there is the problem of transport, which means that it has to be mounted on site, making it much more expensive due to the many parts that the structure comprises that must be mounted on site with a high precision, requiring the use of moulds.
To resolve this problem there are some solar collectors that use a lattice support structure formed by four identical grids, in twos and pre-mounted, each one being formed by a frame and a distribution of uprights and diagonal members within said frame, which have to be subsequently joined together on site but which present the drawbacks that the grids are difficult to transport, particularly in the case of large sizes, and many rivets or mechanical couplings are needed, making mounting labour intensive, with the consequent high economic cost. Furthermore there is the added difficulty of managing the whole lattice volume that forms the support structure of the solar field, which must be galvanized in special tanks for such dimensions, complicating the logistics of constructing the associated solar field.